Alignment of clinical breast tomosynthesis and mechanical images: the effect of the variation in shift and rotation

Simultaneous digital breast tomosynthesis and mechanical imaging (DBTMI), a novel screening approach, combines anatomic DBT with functional analysis of the stress distribution on the compressed breast by mechanical imaging (MI). Preliminary studies suggest potential to reduce false positive findings. DBTMI requires to align DBT and MI images. In this study, we have analyzed robustness to alignment variations in clinical DBTMI data. Our preliminary retrospective analysis included DBTMI of 31 women recalled from screening. We analyzed two aspects of image alignment: rotation and shift. To analyze the shift, we varied the position of suspected abnormality for ±1cm in horizontal or vertical direction. To analyze the rotation, we varied the angle by ±1 degree between radiographic and MI images of 18 women. We compared the relative mean pressure at the lesion area (RMPA) before and after variation. Varying the shift, we observed 14.3%±12.2% difference in RMPA. Averaged separately over biopsy confirmed benign and malignant lesions, 16.2%±14.3% and 12.4%±10.2% difference was observed, respectively. In nine of 31 analyzed datasets, the shift could potentially change the clinical findings. Varying the rotation, we observed 6.4%±4.9% difference in RMPA. Averaged over biopsy confirmed benign and malignant lesions, yielded 5.8%±4.5% and 6.4%±4.8% difference, respectively. In two of 18 DBTMI datasets, the rotational variation could change the clinical findings. The larger effect of the shift may be caused by a relatively large shift variation (±1 cm) compared to the size of detected abnormalities. Analysis of more clinical DBTMI datasets and simulation studies are ongoing.